1. Field of the Invention
The invention relates to a method for fabricating a UV lamp for treating waste gas and to a UV lamp for treating waste gases fabricated therefrom, which is designed and fabricated based on solgel coating techniques by coating a sol of photocatalytic materials on a glass-fiber-cloth, and/or then impreganate this cloth with oxidation catalysts and finally, wrap and fix this cloth on a UV lamp. The invention relates also to a process for treating waste gases by using said UV lamp for treating waste gas through irradiating UV light therefrom on the surface of such photocatalytic materials to generate free electron and electron hole pairs which can decompose waste gases such as organic or inorganic pollutants in the air into unharmful gases.
2. Description of the Prior Art
Solgel techniques have been emphasized today by technically advanced countries for several main reasons. Developments of traditional chemical and physical technologies have met bottle-necks, and in particular, inorganic materials produced through traditional techniques can no longer satisfy requirements, especially, for thin film coating. Materials having multiple components and special structures that cannot be coated by conventional physical and/or chemical methods, as well as when coating those materials on irregularly curved surfaces, such cannot be achieved by conventional evaporative disposition techniques. The solgel technique, on the other hand, can easily generate a metal oxide film, and at the same time, it is the characteristic feature of the solgel technique that a photocatalytic film obtained thereby has a porous crystallite structure required for photocatalytic action. Therefore, solgel coating techniques have become one of the most interesting techniques for research and development in the latter part of the twentieth century.
Recently, preparation of catalysts by solgel techniques also received emphasis by chemical industries, and in particular, photocatalytic techniques is the most important one, including the early developed photocatalytic powders for treating waste water, such as. For example, Robat A. Clyde, U.S. Pat. No. 4,446,236; Robat E. Hetrick Ford Motor Company, U.S. Pat. No. 4,544,470; Yashiaki Harada et al., Osaka Gas Company, U.S. Pat. No. 4,699,720; Tomoji Kawai, et al., Nomura Micro Science Co., U.S. Pat. No. 4,863,608; David G. Ritchie, U.S. Pat. No. 5,069,885; Gerald Cooper, et al., Photo Catalytics Inc., U.S. Pat. Nos. 5,116,582; 5,118,422; 5,174,877; and 5,294,315; Adam Heller, et al., Board of Regents, The University of Texas System, U.S. Pat. No. 5,256,616; Ali Safarzedeh-Amiri, Cryptonics Corporation, U.S. Pat. No. 5,266,214; Fausto Miano and Borgarello, Eniricerche S.p.a., U.S. Pat. No. 5,275,741; Nancy S. Foster et al., Regents of the University of Colorado, U.S. Pat. No. 5,332,508; Ivan Wlassics et al., Ausimont S.p.a., U.S. Pat. No. 5,382,337; Paul C. Melanson and James A. Valdez, Anatol Corporation, U.S. Pat. No. 5,395,522; Henry G. Peebles III et al., American Energy Technology, Inc., U.S. Pat. No. 5,449,466; Brain E. Butters and Anthony L. Powell, Purific Environmental Technologies, Inc., U.S. Pat. Nos. 5,462,674; 5,554,300; and 5,589,078; Yin Zhang, et al., Board of Control of Michigan Technology University, U.S. Pat. No. 5,501,801; Clovis A. Linkous, University of Central Florida, U.S. Pat. No. 5,518,992; and Eiji Normura and Tokuo Suita, Ishihara Sanyo Kaisha Ltd,. U.S. Pat. No. 5,541,096.
The above-mentioned U.S. patents relate chiefly to water treatments, which in the case of granular catalysts, a filtration recovering apparatus is invariably used, and it is of the most importance that such photocatalysis needs sufficient dissolved oxygen in water, otherwise, an aerating operation must carry out for supplying oxygen required by the photocatalytic degradation.
Since then, photocatalysts were used also for treating waste gases, such as those described in, for example, Gregory B. Roupp and Lynette A. Dibble, Arizona State University, U.S. Pat. No. 5,045,288; Jeffrey g. Sczechowski et al., The University of Colorado, U.S. Pat. No. 5,439,652; William A. Jacoby and Danial M. Blake, U.S. Pat. No. 5,449,443; Zhenyyu Zhang and James R. Fehlner, Inrad, U.S. Pat. No. 5,468,699; and Franz D. Oeste, Olga Dietrich Neeleye, U.S. Pat. No. 5,480,524.
The above-mentioned patents relate originally to treatment of waste gases, and basically, were carried out in a closed reactor, and therefore, utilization or operation of granular catalysts or catalysts coating granules usually needed, in general, complicate equipments.
The above-described disadvantages made the prior art photocatalysts difficult to apply for treating polluted air in our living environment. Among them, the only waste water and/or waste gas disposal photocatalytic reactor comprises a UV lamp wrapped with a photocatalyst coated film having fibers as supports therefor was the one described in U.S. Pat. No. 4,982,712 to Michael K. Robertson and Robert B. Henderson, Nutech Energy Systems Inc. As above mentioned, such reactor was a closed type such that counterflowing must be forced by a blower which made such reaction system inconvenient to practice in our living environment.
As for the use of a UV lamp for treating waste gases, it is generally based on the sustained oxidative degradation of organic and/or inorganic hazardous materials in the air by a photocatalytic reaction, to render them into non-harmful substances such as water or carbon dioxide. Since the photocatalytic reaction takes place on the catalyst through UV irradiating of hazardous waste gases and oxygen, it is inactive in cases where the UV light can not reach the catalyst. Accordingly, only the catalyst in the extremely thin top layer (less than one micron) that received UV light becomes active under such conditions. Therefore, in practice, a film coating of photocatalysts on carry substrate materials which are transmittable to UV light are used to prepare a photocatalyst film.
Photocatalytic action can be effected only in the case of direct UV irradiation on coating, while it is inactive in the case of backside irradiation. The reason therefor relates to the fact that electron hole pairs generated during UV irradiation on the surface of photocatalyst will combine in an extremely short time period (microseconds) and releases thermal energy before reacting with oxygen and/or materials to be reacted.
Nevertheless, a photoelectric-chemical catalyst having an electroconductive layer incorporated in the coating film structure can transfer electron generated during UV irradiating via the conductor therein to the positive electrode, such that the electron hole can be retained and the persisting time period of reactive positions can be postponed and thereby improves the efficiency of UV irradiation. However, such coating film is not easy to fabricate and practice. Consequently, it is essential for photocatalytical reaction to take place in simultaneous presence of oxygen, moisture, reactants and catalysts as well as in combination with UV irradiation to give rise the oxidative degradation.
Since the effective thickness of photocatalysts is extremely small, it is sufficient for a layer of photcatalytic material having a thickness of less than 1 micron to be deposited on a UV transmittable substrate by a solgel coating technique. Because photocatalytic materials are in general metal oxides, it is conventional to use vacuum deposition, redox plating, and aqueous precipitation/adsorption coating techniques to form a thin film. Among them, the vacuum deposition technique is usually employed for depositing on the surface of a flat structure, which cannot meet the practical requirement in this field. Furthermore, since vacuum deposition is not capable of obtaining a porous structure of catalysts and a crystalline structure having photcatalytic action, it becomes useless therefor. The aqueous precipitation/adsorption coating technique consists of precipitating a photocatalytic metal oxide on the surface of a substrate. However, because the bonding strength between the catalyst thus adsorbed and the surface of the substrate is generally not strong enough, the coating peels easily and is not durable. As for redox plating, titanium metal or alloy thereof has been used to form a titanium dioxide thin film under oxidation conditions at high temperature; however, since the substrate is an opaque metal and the surface area of the catalyst film thus obtained is insufficient, the photocatalytic efficiency is too poor to be practical.
As stated previously, since the solgel coating technique can generate easily a coating film on an irregular surface structure as well as can produce a porous crystallite structure required by the photocatalytical action, and also from the view of the inherent feature of the photocatalytical reaction, the present inventors adopt the solgel coating technique for fabricating the UV lamp for treating waste gases according to the invention.
As for the solgel coating technique, in general, a metal alkoxide such as Ti(OR)4, wherein R is a hydrocarbyl group, CnH2n+1, where n=1xcx9c5, and is, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl, sec-butyl, pentyl and the like; is used as the main component in admixture with organic and/or inorganic salts of other metals such as W, Zn, Sn, and Fe and undergoes hydrolytic condensation in an alcohol solvent to form an organic metal polymer which is dissolved in that alcohol solution as a sol. Amounts of alkoxide, water, additives and solvent can be adjusted depending to the requirement of coating to form the desired film.
As the substrate used in the solgel coating technique, glass fiber woven cloth can provide an increased surface area of photocatalysts and can allow waste gases in the air to diffuse readily in the photocatalytic active sites. The glass fiber woven cloth can be the one conventionally used in production of printed circuit boards, which, in general, has a fiber diameter of 10xcx9c100 xcexc, fiber number of 1xcx9c10, and porosity of 100xcx9c100 mesh. The glass fiber woven cloth can be reinforced with a silane. In addition to glass fiber, other materials such as quartz, ceramics or metal can be used as the substrate.
Then, the glass fiber cloth can be impregnated batchwise or continuously with the photocatalyst sol by a roller, wherein, through controlling the drawing speed of the cloth and the humidity and temperature in the air, an uniform layer (0.1xcx9c1.0xcexc) of photocatalyst coating can he applied on the surface of the glass fiber cloth. The coated fiber cloth is undergone a hydrolysis in the air for 1xcx9c10 minutes, baked at a temperature of 100xcx9c200xc2x0 C. for 10xcx9c30 minutes, sintered at high temperature of 400xcx9c600xc2x0 C. for 10xcx9c120 minutes and thereafter, cooled for 10xcx9c120 minutes to a temperature below 200xc2x0 C. to produce a photocatalyst-coated glass fiber cloth.
In the production of the above-described photocatalyst-coated glass fiber cloth, in order to improve the efficiency of treating waste gases, it can be soaked with a aqueous solution containing metal salts having oxidative catalytic action. Such metal salts include precious metal such as inorganic salts of Pd, Pt, Au and Ag or inorganic salts of transition metal such as Mo, Nb, V, Ce or Cr. The glass fiber cloth is ready for use after being soaked with oxidative catalyst after dried.
For use of the above-said photocatalyst and/or oxidative catalyst-coated glass fiber cloth in production of the UV lamp for treating waste gases, they can be tailored into a size depending on the length or size of the UV lamp and the number of wrapping layer required. In general, the number of layer is to achieve an UV blocking of above 99%, and normally, is 2xcx9c3 layers. After wrapping around the UV lamp, it is fixed by UV resistant glue, or seamed by laser sintering.
Suitable UV lamp is the common UV lamp, including those having wavelength of 254, 312 or 365 nm. Among them, UV lamps having wavelength of 254 and 312 nm Shuld employ SiO2 quartz and thus have high production costs, whereas the one having wavelength of 365 nm can be produced with soda lime glass tubes and has a low cost. Depending on the type of waste gases treatments, a UV lamp of 254 nm can he used for the case requiring higher energy for degrading waste gases and those of 365 nm can be used for the photocatalytic degradation of common waste gases. The UV lamp of 365 nm is known as mosquito-capturing lamp, whereas the UV lamp of 254 nm is known as sterilizng lamp. Therefore, if the 365 nm UV lamp is wrapped with topical or a single layer of a photocatalyst-coated glass fiber cloth, it can function both as waste gas treating and mosquito-capturing; whereas the 254 in UV lamp is wrapped with topical or a single layer of a photocatalyst-coated glass fiber cloth, it can function both as waste gas treating and sterilization.
Accordingly, in one aspect, the invention provides a process for coating photocatalyst on a glass fiber woven cloth, which comprising (1) formulating a photocatalyst coating-forming sol; (2) dip coating a glass fiber cloth with a photocatalyst sol; (3) drying and sintering into a coating having photocatalytic function; (4) impregnating said photocatalyst-coated glass fiber cloth with a solution of an oxidation catalyst; and (5) drying again to form a photocatalyst-coated glass fiber cloth.
In another aspect, the invention provides a process for fabricating a UV lamp for treating waste gas, which is designed and fabricated through solgel techniques by coating photocatalytic materials on a quartz-or glass-fiber-cloth, sintering this photocatalytic material-coated fiber cloth at high temperature into a structure having photocatalytic action, and then wrapping this cloth on a UV lamp.
In still another aspect, the invention provides a UV lamp for treating waste gases, which is fabricated by the above-described process
In yet another aspect, the invention provides a method for treating waste gases in the air by using the above-said UV lamp through irradiating UV light on the surface of such photocatalytic materials to generate free electron and electron hole pairs which can decompose waste gases in the air into harmless products.